Time-multiplexed backlight and multiview display using same

ABSTRACT

Time-multiplexed backlighting includes a time-multiplexed light source to provide a light beam having a first non-zero propagation angle during a first time interval and a second non-zero propagation angle during a second time interval. A time-multiplexed backlight includes a light guide configured to guide the light beam and a diffraction grating configured to coupled out a portion of the guided light beam with a different principal angular direction in each of the first time interval and the second time interval. A multiview display includes the time-multiplexed light source and a multibeam backlight to provide coupled-out light beams during each of the first and second time intervals, wherein the principal angular directions of the coupled-out light beams correspond to different view directions of the multiview display.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation patent application of and claims thebenefit of priority to International Application No. PCT/US2016/025423,filed Mar. 31, 2016, which claims priority to U.S. Provisional PatentApplication Ser. No. 62/214,977, filed Sep. 5, 2015, the entire contentsof both are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

N/A

BACKGROUND

Electronic displays are a nearly ubiquitous medium for communicatinginformation to users of a wide variety of devices and products. Amongthe most commonly found electronic displays are the cathode ray tube(CRT), plasma display panels (PDP), liquid crystal displays (LCD),electroluminescent displays (EL), organic light emitting diode (OLED)and active matrix OLEDs (AMOLED) displays, electrophoretic displays (EP)and various displays that employ electromechanical or electrofluidiclight modulation (e.g., digital micromirror devices, electrowettingdisplays, etc.). In general, electronic displays may be categorized aseither active displays (i.e., displays that emit light) or passivedisplays (i.e., displays that modulate light provided by anothersource). Among the most obvious examples of active displays are CRTs,PDPs and OLEDs/AMOLEDs. Displays that are typically classified aspassive when considering emitted light are LCDs and EP displays. Passivedisplays, while often exhibiting attractive performance characteristicsincluding, but not limited to, inherently low power consumption, mayfind somewhat limited use in many practical applications given the lackof an ability to emit light.

To overcome the limitations of passive displays associated with emittedlight, many passive displays are coupled to an external light source.The coupled light source may allow these otherwise passive displays toemit light and function substantially as an active display. Examples ofsuch coupled light sources are backlights. A backlight may serve as asource of light (often a panel backlight) that is placed behind anotherwise passive display to illuminate the passive display. Forexample, a backlight may be coupled to an LCD or an EP display. Thebacklight emits light that passes through the LCD or the EP display. Thelight emitted is modulated by the LCD or the EP display and themodulated light is then emitted, in turn, from the LCD or the EPdisplay. Often backlights are configured to emit white light. Colorfilters are then used to transform the white light into various colorsused in the display. The color filters may be placed at an output of theLCD or the EP display (less common) or between the backlight and the LCDor the EP display, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features of examples and embodiments in accordance with theprinciples described herein may be more readily understood withreference to the following detailed description taken in conjunctionwith the accompanying drawings, where like reference numerals designatelike structural elements, and in which:

FIG. 1A illustrates a perspective view of a multiview display in anexample, according to an embodiment consistent with the principlesdescribed herein

FIG. 1B illustrates a graphical representation of the angular componentsof a light beam having a particular principal angular directioncorresponding to a view direction of a multiview display in an example,according to an embodiment consistent with the principles describedherein.

FIG. 2 illustrates a cross sectional view of a diffraction grating in anexample, according to an embodiment consistent with the principlesdescribed herein.

FIG. 3A illustrates a cross sectional view of a time-multiplexedbacklight in an example, according to an embodiment consistent with theprinciples described herein.

FIG. 3B illustrates a cross sectional view of a portion of atime-multiplexed backlight in an example, according to anotherembodiment consistent with the principles described herein.

FIG. 3C illustrates a cross sectional view of another portion of atime-multiplexed backlight in an example, according to anotherembodiment consistent with the principles described herein.

FIG. 4A illustrates a schematic view of a time-multiplexed light sourcein an example, according to an embodiment consistent with the principlesdescribed herein.

FIG. 4B illustrates a schematic view of a time-multiplexed light sourcein an example, according to another embodiment consistent with theprincipals described herein.

FIG. 5A illustrates a cross sectional view of a multibeam diffractiongrating in an example, according to an embodiment consistent with theprinciples described herein.

FIG. 5B illustrates a perspective view of a multibeam diffractiongrating in an example, according to an embodiment consistent with theprinciples described herein.

FIG. 6 illustrates a block diagram of a multiview display in an example,according to an embodiment consistent with the principles describedherein.

FIG. 7 illustrates a flow chart of a method of time-multiplexedbacklight operation in an example, according to an embodiment consistentwith the principles described herein.

Certain examples and embodiments may have other features that are one ofin addition to and in lieu of the features illustrated in theabove-referenced figures. These and other features are detailed belowwith reference to the above-referenced figures.

DETAILED DESCRIPTION

Embodiments in accordance with the principles described herein providetime-multiplexed display backlighting. In particular, backlighting of adisplay (e.g., an electronic display) employs a time-multiplexed lightsource to provide a light beam having different angles of propagationduring different intervals of time. Light of the light beam may becoupled-out of a backlight as an emitted or coupled-out light beam thatis directed in a viewing direction of the display. According to variousembodiments, the coupled-out light beam may have a principal angulardirection corresponding to or that is determined by the light beampropagation angle. As such, the coupled-out light beam may havedifferent, albeit predetermined, principal angular directions in thedifferent time intervals, according to various embodiments. Timemultiplexing may enable switching between the different principalangular directions as a function of time, for example.

According to some embodiments of the principles described herein, aplurality of coupled-out light beams may be provided by the backlightfrom the light beam of the time-multiplexed light source. Coupled-outlight beams of the plurality may have different principal angulardirections from one another. The coupled-out light beams having thedifferent principal angular directions (also referred to as ‘thedifferently directed light beams’) may be employed to displayinformation including three-dimensional (3D) or multiview information.In particular, the different principal angular directions of thecoupled-out light beam plurality may correspond to various viewdirections of different views of a 3D or multiview display (e.g., a‘glasses free’ or autostereoscopic electronic display). Further, thedifferently directed coupled-out light beams may be modulated and serveas pixels of the different views of the multiview display.

Moreover, the plurality of coupled-out light beams and different viewscorresponding thereto provided from the light beam of thetime-multiplexed light source may have different directions in differenttime intervals. In particular, sets of coupled-out light beams of theplurality and corresponding sets of different views provided during thedifferent time intervals according to time multiplexing of the lightsource may be angularly interleaved with one another, in someembodiments. Angular interleaving of coupled-out light beams anddifferent views of the sets may effectively increase one or both of apixel resolution and a view resolution of the display, according tovarious embodiments.

Herein, a 3D or multiview display is defined as an electronic display ordisplay system configured to provide different views of a multiviewimage in different view directions. FIG. 1A illustrates a perspectiveview of a multiview display 10, according to an example consistent withthe principles described herein. As illustrated in FIG. 1A, themultiview display 10 comprises a screen 12 that is viewed in order tosee a 3D or multiview image. The multiview display 10 provides differentviews 14 of the multiview image in different view directions 16 relativeto the screen 12. The view directions 16 are illustrated as arrowsextending from the screen 12 in various different principal angulardirections; the different views 14 are illustrated as shaded polygonalboxes at the termination of the arrows (i.e., depicting the viewdirections 16); and only four views 14 and four view directions 16 areillustrated, all by way of example and not limitation. Note that whilethe different views 14 are illustrated in FIG. 1A as being above thescreen, the views 14 actually appear on or in a vicinity of the screen12 when the multiview image is displayed on the multiview display 10.Depicting the views 14 above the screen 12 is only for simplicity ofillustration meant to represent viewing the multiview display 10 from arespective one of the view directions 16 corresponding to a particularview 14.

A view direction or equivalently a light beam having a directioncorresponding to a view direction of a multiview display generally has aprincipal angular direction given by angular components {θ, ϕ}, bydefinition herein. The angular component θ is referred to herein as the‘elevation component’ or ‘elevation angle’ of the light beam. Theangular component ϕ is referred to as the ‘azimuth component’ or‘azimuth angle’ of the light beam. By definition, the elevation angle θis an angle in a vertical plane (e.g., perpendicular to a plane of themultiview display screen while the azimuth angle ϕ is an angle in ahorizontal plane (e.g., parallel to the multiview display screen plane).FIG. 1B illustrates a graphical representation of the angular components{θ, ϕ} of a light beam 20 having a particular principal angulardirection corresponding to a view direction of a multiview display,according to an example of the principles described herein. In addition,the light beam 20 is emitted or emanates from a particular point, bydefinition herein. That is, by definition, the light beam 20 has acentral ray associated with a particular point of origin within themultiview display. FIG. 1B also illustrates the light beam (or viewdirection) point of origin O.

Referring again to FIG. 1A, also illustrated are other views 14′ (e.g.,a second set of views) with corresponding view directions 16′. The otherviews 14′ are polygonal boxes shaded with dashed-dot shading at the endof the dashed-line corresponding view direction 16′ arrows to furtherdistinguish from the first mentioned views 14. The other views 14′ maybe views of the multiview display provided during a second timeinterval, while the views 14 (e.g., a first set of views) may be viewsof multiview display provided during a first time interval, for example.Further, as illustrated, the other views 14′ and the other viewdirections 16′ are angularly interleaved with the views 14 and thecorresponding view directions 16. Note that in FIG. 1A, solid linesillustrating the views 14 and the view directions 16 represent theseelements during the first time interval, while dashed lines of the otherviews 14′ and the other view directions 16′ represent these elementsduring the second time interval. Note that while reference is madeherein to a ‘first’ time interval and a ‘second’ time interval, ingeneral any number of time intervals may be used. As such, there mayalso be a third time interval, a fourth time interval and so on. Herein,reference is confined to ‘first’ and ‘second’ for ease of discussion andnot by way of limitation.

Herein, ‘multiview’ as used in the terms ‘multiview image’ and‘multiview display’ is defined as a plurality of views representingdifferent perspectives or including angular disparity between views ofthe view plurality. Further, the term ‘multiview’ by definitionexplicitly includes more than two different views (i.e., a minimum ofthree views and generally more than three views). As such, ‘multiview’as employed herein is explicitly distinguished from stereoscopic viewsthat include only two different views to represent a scene. Notehowever, while multiview images and multiview displays include more thantwo views, by definition herein, multiview images may be viewed (e.g.,on a multiview display) as a stereoscopic pair of images by selectingonly two of the multiview views to view at a time (e.g., one view pereye).

Herein, a ‘light guide’ is defined as a structure that guides lightwithin the structure using total internal reflection. In particular, thelight guide may include a core that is substantially transparent at anoperational wavelength of the light guide. In various examples, the term‘light guide’ generally refers to a dielectric optical waveguide thatemploys total internal reflection to guide light at an interface betweena dielectric material of the light guide and a material or medium thatsurrounds that light guide. By definition, a condition for totalinternal reflection is that a refractive index of the light guide isgreater than a refractive index of a surrounding medium adjacent to asurface of the light guide material. In some embodiments, the lightguide may include a coating in addition to or instead of theaforementioned refractive index difference to further facilitate thetotal internal reflection. The coating may be a reflective coating, forexample. The light guide may be any of several light guides including,but not limited to, one or both of a plate or slab guide and a stripguide.

Further herein, the term ‘plate’ when applied to a light guide as in a‘plate light guide’ is defined as a piece-wise or differentially planarlayer or sheet, which is sometimes referred to as a ‘slab’ guide. Inparticular, a plate light guide is defined as a light guide configuredto guide light in two substantially orthogonal directions bounded by atop surface and a bottom surface (i.e., opposite surfaces) of the lightguide. Further, by definition herein, the top and bottom surfaces areboth separated from one another and may be substantially parallel to oneanother in at least a differential sense. That is, within anydifferentially small section of the plate light guide, the top andbottom surfaces are substantially parallel or co-planar.

In some embodiments, the plate light guide may be substantially flat(i.e., confined to a plane) and therefore, the plate light guide is aplanar light guide. In other embodiments, the plate light guide may becurved in one or two orthogonal dimensions. For example, the plate lightguide may be curved in a single dimension to form a cylindrical shapedplate light guide. However, any curvature has a radius of curvaturesufficiently large to insure that total internal reflection ismaintained within the plate light guide to guide light.

Herein, a ‘diffraction grating’ is generally defined as a plurality offeatures (i.e., diffractive features) arranged to provide diffraction oflight incident on the diffraction grating. In some examples, theplurality of features may be arranged in a periodic or quasi-periodicmanner. For example, the diffraction grating may include a plurality offeatures (e.g., a plurality of grooves or ridges in a material surface)arranged in a one-dimensional (1D) array. In other examples, thediffraction grating may be a two-dimensional (2D) array of features. Thediffraction grating may be a 2D array of bumps on or holes in a materialsurface, for example.

As such, and by definition herein, the ‘diffraction grating’ is astructure that provides diffraction of light incident on the diffractiongrating. If the light is incident on the diffraction grating from alight guide, the provided diffraction or diffractive scattering mayresult in, and thus be referred to as, ‘diffractive coupling’ in thatthe diffraction grating may couple light out of the light guide bydiffraction. The diffraction grating also redirects or changes an angleof the light by diffraction (i.e., at a diffractive angle). Inparticular, as a result of diffraction, light leaving the diffractiongrating generally has a different propagation direction than apropagation direction of the light incident on the diffraction grating(i.e., incident light). The change in the propagation direction of thelight by diffraction is referred to as ‘diffractive redirection’ herein.Hence, the diffraction grating may be understood to be a structureincluding diffractive features that diffractively redirects lightincident on the diffraction grating and, if the light is incident from alight guide, the diffraction grating may also diffractively couple outthe light from the light guide.

Further, by definition herein, the features of a diffraction grating arereferred to as ‘diffractive features’ and may be one or more of at, inand on a material surface (i.e., a boundary between two materials). Thesurface may be a surface of a light guide, for example. The diffractivefeatures may include any of a variety of structures that diffract lightincluding, but not limited to, one or more of grooves, ridges, holes andbumps at, in or on the surface. For example, the diffraction grating mayinclude a plurality of substantially parallel grooves in the materialsurface. In another example, the diffraction grating may include aplurality of parallel ridges rising out of the material surface. Thediffractive features (e.g., grooves, ridges, holes, bumps, etc.) mayhave any of a variety of cross sectional shapes or profiles that providediffraction including, but not limited to, one or more of a sinusoidalprofile, a rectangular profile (e.g., a binary diffraction grating), atriangular profile and a saw tooth profile (e.g., a blazed grating).

By definition herein, a ‘multibeam diffraction grating’ is a diffractiongrating that produces diffractively redirected light (e.g.,diffractively coupled-out light) that includes a plurality of lightbeams. The light beams of the plurality produced by a multibeamdiffraction grating have different principal angular directions from oneanother, by definition herein. In particular, by definition, a lightbeam of the plurality has a predetermined principal angular directionthat is different from another light beam of the light beam plurality asa result of diffractive coupling and diffractive redirection of incidentlight by the multibeam diffraction grating. The light beam plurality mayrepresent a light field. For example, the light beam plurality mayinclude eight light beams that have eight different principal angulardirections. The eight light beams in combination (i.e., the light beamplurality) may represent the light field, for example. According tovarious embodiments, the different principal angular directions of thevarious light beams are determined by a combination of a grating pitchor spacing and an orientation or rotation of the diffractive features ofthe multibeam diffraction grating at points of origin of the respectivelight beams relative to a propagation direction or angle of the lightincident on the multibeam diffraction grating.

According to various embodiments described herein, a diffraction grating(e.g., a multibeam diffraction grating) is employed to producecoupled-out light that represents pixels of an electronic display orsimply a ‘display.’ In particular, the light guide having a multibeamdiffraction grating to produce the light beams of the plurality havingdifferent principal angular directions may be part of a backlight of orused in conjunction with a display such as, but not limited to, a‘glasses free’ multiview display (also sometimes referred to as a‘holographic’ display or an autostereoscopic display). As such, thedifferently directed light beams produced by coupling out guided lightfrom the light guide using the multibeam diffractive grating may be orrepresent ‘pixels’ of the multiview display. Moreover, as describedabove, the differently directed light beams may form a light fieldincluding directions corresponding to view directions of the multiviewdisplay.

According to various examples described herein, a diffraction grating(e.g., a multibeam diffraction grating) may be employed to diffractivelyscatter or couple light out of a light guide (e.g., a plate light guide)as a light beam. In particular, a diffraction angle θ_(m) of or providedby a locally periodic diffraction grating may be given by equation (1)as:

$\begin{matrix}{\theta_{m} = {\sin^{- 1}\left( {{n\; \sin \; \theta_{i}} - \frac{m\; \lambda}{d}} \right)}} & (1)\end{matrix}$

where λ is a wavelength of the light, m is a diffraction order, n is anindex of refraction of a light guide, d is a distance between featuresof the diffraction grating, θ_(i) is an angle of incidence of light onthe diffraction grating. For simplicity, equation (1) assumes that thediffraction grating is adjacent to a surface of the light guide and arefractive index of a material outside of the light guide is equal toone (i.e., n_(out)=1). In general, the diffraction order m is given byan integer. According to various examples, a diffraction angle θ_(m) ofa light beam produced by the diffraction grating may be given byequation (1) where the diffraction order is positive (e.g., m>0). Forexample, first-order diffraction is provided when the diffraction orderm is equal to one (i.e., m=1).

FIG. 2 illustrates a cross sectional view of a diffraction grating 30 inan example, according to an embodiment consistent with the principlesdescribed herein. For example, the diffraction grating 30 may be locatedon a surface of a light guide 40. In addition, FIG. 2 illustrates alight beam 20 incident on the diffraction grating 30 at an incidentangle θ_(i). The light beam 20 is a guided time-multiplexed light beamwithin the light guide 40. Also illustrated in FIG. 2 is a coupled-outlight beam 50 diffractively produced and coupled-out by the diffractiongrating 30 as a result of the incident light beam 20. The coupled-outlight beam 50 has a diffraction angle θ_(m) (or principal angulardirection) as given by equation (1). The coupled-out light beam 50 maycorrespond to a diffraction order ‘m’ of the diffraction grating 30, forexample.

Herein a ‘collimator’ is defined as substantially any optical device orapparatus that is configured to collimate light. For example, acollimator may include, but is not limited to, a collimating mirror orreflector, a collimating lens, and various combinations thereof. In someembodiments, the collimator comprising a collimating reflector may havea reflecting surface characterized by a parabolic curve or shape. Inanother example, the collimating reflector may comprise a shapedparabolic reflector. By ‘shaped parabolic’ it is meant that a curvedreflecting surface of the shaped parabolic reflector deviates from a‘true’ parabolic curve in a manner determined to achieve a predeterminedreflection characteristic (e.g., a degree of collimation). Similarly, acollimating lens may comprise a spherically shaped surface (e.g., abiconvex spherical lens).

In some embodiments, the collimator may be a continuous reflector or acontinuous lens (i.e., a reflector or a lens having a substantiallysmooth, continuous surface). In other embodiments, the collimatingreflector or the collimating lens may comprise a substantiallydiscontinuous surface such as, but not limited to, a Fresnel reflectoror a Fresnel lens that provides light collimation. According to variousembodiments, an amount of collimation provided by the collimator mayvary in a predetermined degree or amount from one embodiment to another.Further, the collimator may be configured to provide collimation in oneor both of two orthogonal directions (e.g., a vertical direction and ahorizontal direction). That is, the collimator may include a shape orshaped surface in one or both of two orthogonal directions that provideslight collimation, according to some embodiments.

Herein, a ‘light source’ is defined as a source of light (e.g., anoptical emitter configured to produce and emit light). For example, thelight source may comprise an optical emitter such as a light emittingdiode (LED) that emits light when activated or turned on. In particular,herein the light source may be substantially any source of light orcomprise substantially any optical emitter including, but not limitedto, one or more of a light emitting diode (LED), a laser, an organiclight emitting diode (OLED), a polymer light emitting diode, aplasma-based optical emitter, a fluorescent lamp, an incandescent lamp,and virtually any other source of light. The light produced by the lightsource may have a color (i.e., may include a particular wavelength oflight), or may be a range of wavelengths (e.g., white light). In someembodiments, the light source may comprise a plurality of opticalemitters. For example, the light source may include a set or group ofoptical emitters in which at least one of the optical emitters produceslight having a color, or equivalently a wavelength, that differs from acolor or wavelength of light produced by at least one other opticalemitter of the set or group. The different colors may include primarycolors (e.g., red, green, blue) for example.

Further, as used herein, the article ‘a’ is intended to have itsordinary meaning in the patent arts, namely ‘one or more’. For example,‘a grating’ means one or more gratings and as such, ‘the grating’ means‘the grating(s)’ herein. Also, any reference herein to ‘top’, ‘bottom’,‘upper’, ‘lower’, ‘up’, ‘down’, ‘front’, ‘back’, ‘first’, ‘second’,‘left’ or ‘right’ is not intended to be a limitation herein. Herein, theterm ‘about’ when applied to a value generally means within thetolerance range of equipment used to produce the value, or may mean plusor minus 10%, or plus or minus 5%, or plus or minus 1%, unless otherwiseexpressly specified. Further, the term ‘substantially’ as used hereinmeans a majority, or almost all, or all, or an amount within a range ofabout 51% to about 100%. Moreover, examples herein are intended to beillustrative only and are presented for discussion purposes and not byway of limitation.

In accordance with some embodiments of the principles described herein,a time-multiplexed backlight is provided. FIG. 3A illustrates a crosssectional view of a time-multiplexed backlight 100 in an example,according to an embodiment consistent with the principles describedherein. FIG. 3B illustrates a cross sectional view of a portion of atime-multiplexed backlight 100 in an example, according to anotherembodiment consistent with the principles described herein. FIG. 3Cillustrates a cross sectional view of another portion of atime-multiplexed backlight 100 in an example, according to anotherembodiment consistent with the principles described herein.

According to various embodiments, light coupled out from thetime-multiplexed backlight 100 may form or provide an emitted or‘coupled-out’ light beam 102 directed away from a surface of thetime-multiplexed backlight 100. Moreover, the coupled-out light beam 102may be directed away from the surface in different principal angulardirections during different time intervals. For example, the coupled-outlight beam 102 may be time-multiplexed to have a first principal angulardirection in or during a first time interval and a second principalangular direction during a second time interval. In particular, theprincipal angular direction of the coupled-out light beam 102 istime-multiplexed, according to various embodiments.

FIGS. 3A and 3B depicts the coupled-out light beam 102 during a firsttime interval using a solid arrow, while a dashed arrow depicts thecoupled-out light beam 102 during a second time interval. In particular,FIG. 3A illustrates a plurality of coupled-out light beams 102, wherethe coupled-out light beams 102 in the first time interval are angularlyinterleaved with the coupled-out light beams 102 in the second timeinterval. FIG. 3B illustrates a single coupled-out light beam 102 havinga different principal angular direction in each of the first timeinterval and the second time interval.

Note that while specific reference is made above to a ‘first’ non-timeinterval and a ‘second’ time interval, in general there may be aplurality of time intervals and corresponding different coupled-outlight beams 102 in different time intervals of the plurality. As such,for example, there may also be a third time interval, a fourth timeinterval and so on with corresponding coupled-out light beams 102.Herein, reference is confined to ‘first’ and ‘second’ for ease ofdiscussion and not by way of limitation.

In some embodiments (as described below), the time-multiplexed backlight100 may be a grating-based backlight. For example, diffraction mayprovide diffractive coupling of light out of the time-multiplexedbacklight 100. That is, a diffraction grating may be employed to coupleout the light as the coupled-out light beam 102. In other embodiments,the light may be coupled or scattered out as the coupled-out light beam102 in another manner including, but not limited to, reflectivescattering.

Moreover, the principal angular directions of coupled-out light beams102 of the plurality may be time-multiplexed (i.e., may differ indifferent time intervals). In particular, in some embodiments describedin more detail below with respect to the time-multiplexed backlight 100configured as a multibeam backlight and more specifically with respectto a multibeam diffraction grating, the plurality of coupled-out lightbeams 102 may be configured to form a light field. According to variousembodiments, the light field may have different characteristics ordifferent angular components during different time intervals as afunction of or as provided by time multiplexing. For example, differentsets of coupled-out light beams 102 having corresponding different setsof principal angular directions may be provided in different timeintervals by the time-multiplexed backlight 100, as a result of timemultiplexing.

According to various embodiments, the coupled-out light of thecoupled-out light beam 102 includes a portion of light within thetime-multiplexed backlight 100. In particular, the light may be guidedlight or equivalently a guided light beam 104 within thetime-multiplexed backlight 100 (e.g., in a light guide, as describedbelow). As illustrated in FIGS. 3A-3C, a general propagation directionof the guided light beam 104 is illustrated as horizontal bold arrows103 for simplicity of illustration and not by way of limitation.Further, time multiplexing of the principal angular direction of thecoupled-out light beam 102 may be provided through time multiplexing ofa non-zero propagation angle of the guided light beam 104, as isdescribed below in more detail.

In some embodiments, the time-multiplexed backlight 100 may be a sourceof light or a ‘backlight’ of a display (e.g., an electronic display). Inparticular, according to some embodiments where a light field isproduced by the plurality of coupled-out light beams 102, the electronicdisplay may be a so-called ‘glasses free’ multiview electronic display(e.g., a 3D display or autostereoscopic display) in which the variouscoupled-out light beams 102 correspond to or represent pixels associatedwith different ‘views’ of the multiview display. Further, in someembodiments, the coupled-out light beams 102 may be modulated (e.g., bya light valve, as described below). For example, a light valve may beemployed to modulate the coupled-out light beam 102. Modulation ofdifferent sets of coupled-out light beams 102 directed in differentangular directions away from the time-multiplexed backlight 100 may beparticularly useful for dynamic multiview electronic displayapplications. That is, the different sets of modulated coupled-out lightbeams 102 directed in particular view directions may represent dynamicpixels of the multiview electronic display corresponding to theparticular view directions thereof.

The time-multiplexed backlight 100 illustrated in FIGS. 3A-3C comprisesa light guide 110. In some embodiments, the light guide 110 may be aplate light guide. The light guide 110 is configured to guide light as aguided beam of light (i.e., a guided light beam 104). For example, thelight guide 110 may include a dielectric material configured as anoptical waveguide. The dielectric material may have a first refractiveindex that is greater than a second refractive index of a mediumsurrounding the dielectric optical waveguide. The difference inrefractive indices is configured to facilitate total internal reflectionof the guided light according to one or more guided modes of the lightguide 110, for example. In some embodiments, the guided light beam 104may be collimated (i.e., a collimated guided light beam 104).

According to various embodiments, the guided light beam 104 is guided byand along a length of the light guide 110 (e.g., the general directionas illustrated by the bold arrows 103 in FIG. 3A). Further, the lightguide 110 is configured to guide the guided light beam 104 at a non-zeropropagation angle between a first surface 110′ (e.g., ‘front’ surface orside) and a second surface 110″ (e.g., ‘back’ surface or side) of thelight guide 110 using total internal reflection. In particular, theguided light beam 104 propagates by reflecting or ‘bouncing’ between thefirst surface 110′ and the second surface 110″ of the light guide 110 atthe non-zero propagation angle.

As defined herein, a ‘non-zero propagation angle’ is an angle relativeto a surface (e.g., the first surface 110′ or the second surface 110″)of the light guide 110. Further, when referring to light (e.g., theguided light beam 104) guided by the light guide 110, the non-zeropropagation angle is, by definition herein, both greater than zero andless than a critical angle of total internal reflection within the lightguide 110. Moreover, a specific non-zero propagation angle may be chosen(e.g., arbitrarily) for a particular implementation as long as thespecific non-zero propagation angle is chosen to be less than thecritical angle of total internal reflection within the light guide 110.

In some examples, the light guide 110 (e.g., as a plate light guide) maybe a slab or plate optical waveguide comprising an extended,substantially planar sheet of optically transparent, dielectricmaterial. The substantially planar sheet of dielectric material isconfigured to guide the guided light beam 104 using total internalreflection. According to various examples, the optically transparentmaterial of the light guide 110 may include or be made up of any of avariety of dielectric materials including, but not limited to, one ormore of various types of glass (e.g., silica glass,alkali-aluminosilicate glass, borosilicate glass, etc.) andsubstantially optically transparent plastics or polymers (e.g.,poly(methyl methacrylate) or ‘acrylic glass’, polycarbonate, etc.). Insome examples, the light guide 110 may further include a cladding layer(not illustrated) on at least a portion of a surface (e.g., one or bothof the top surface and the bottom surface) of the light guide 110. Thecladding layer may be used to further facilitate total internalreflection, according to some embodiments.

According to various embodiments, light of the guided light beam 104 inthe light guide 110 may be introduced or coupled into the light guide110 at the non-zero propagation angle. One or more of a lens, a mirroror similar reflector (e.g., a tilted collimating reflector), and a prism(not illustrated) may facilitate coupling light into an input end of thelight guide 110 as the guided light beam 104 at the non-zero propagationangle, for example. Once coupled into the light guide 110, the guidedlight beam 104 propagates along the light guide 110 in a direction thatis generally away from the input end (e.g., illustrated by bold arrows103 pointing along an x-axis in FIGS. 3A-3C).

Further, the guided light beam 104 produced by coupling light into thelight guide 110 may be a collimated light beam, according to variousembodiments. Herein, a ‘collimated light’ or ‘collimated light beam’ isdefined as a beam of light in which rays of the light beam aresubstantially parallel to one another within the light beam (e.g., theguided light beam 104). Further, rays of light that diverge or arescattered from the collimated light beam are not considered to be partof the collimated light beam, by definition herein. Collimation of thelight to produce the collimated guided light beam 104 may be provided bya collimator including, but not limited to, the lens or mirror (e.g.,tilted collimating reflector, etc.).

As illustrated in FIGS. 3A and 3C, the time-multiplexed backlight 100further comprises a time-multiplexed light source 120. Thetime-multiplexed light source 120 is configured to provide light as alight beam to the light guide 110. For example, the time-multiplexedlight source 120 may be optically coupled to an input end of the lightguide 110 such that the provided light is communicated to the lightguide 110 through the input end. Further, the time-multiplexed lightsource 120 is configured to provide the light to the light guide 110 asthe guided light beam 104 (respective light beams 104′ and 104″) at afirst non-zero propagation angle during a first time interval and at asecond non-zero propagation angle during a second time interval, whereinthe first non-zero propagation angle and the second non-zero propagationangle are different from one another.

Note that while specific reference is made herein to a ‘first’ non-zeropropagation angle and a ‘second’ non-zero propagation anglecorresponding to the first and second time intervals, respectively, ingeneral there may a plurality of different non-zero propagation angles.In particular, the time-multiplexed light source 120 may be configuredto provide the guided light beam 104 at different non-zero propagationangles of the plurality corresponding to respective different timeintervals of the plurality of time intervals.

In particular, in FIG. 3C, the guided light beam 104′ provided by thetime-multiplexed light source 120 during the first time interval isillustrated using a solid extended arrow. Similarly, the guided lightbeam 104″ provided by the time-multiplexed light source 120 during thesecond time interval is depicted by a dashed extended arrow. Further,FIGS. 3B-3C illustrate the first non-zero propagation angle γ′ and thesecond non-zero propagation angle γ″ of the guided light beams 104′,104″ provided respectively in each of the first and second timeintervals by the time-multiplexed light source 120.

In some embodiments, the first and second time intervals may benon-overlapping intervals of time. That is, the respective guided lightbeam 104 may have at any point in time either, but not both, of thefirst non-zero propagation angle or the second non-zero propagationangle. In other embodiments, the first and second time intervals mayoverlap such that both propagation angles exist simultaneously withinthe light guide 110 for a period of time corresponding to the overlap intime intervals. Note that FIG. 3B illustrates the guided light beam104′, 104″ having both the first non-zero propagation angle γ′ and thesecond non-zero propagation angle γ″ simultaneously incident on thediffraction grating 130, for simplicity of illustration not by way oflimitation.

The time-multiplexed light source 120 may be realized using any ofvariety of different configurations, according to various embodiments.For example, the time-multiplexed light source 120 may include aplurality of optical emitters having locations or positions configuredto provide light at different angles to the light guide 110. Selectivelyswitching the optical emitters of the plurality on and off may providetime multiplexing of the non-zero propagation angle of the guided lightbeam, according to some embodiments. In other examples, an opticalelement of the time-multiplexed light source 120 such as, but notlimited to, a tilted reflector or a collimator (e.g., collimatingreflector or collimating lens) may be configured to selectively changean angle of light from an optical emitter as a function of time in orderto effect time multiplexing of the non-zero propagation angle. In yetother examples, the time-multiplexed light source 120 may include anoptical emitter that is selectively movable or that may be selectivelytilted to provide the different angles of light at an input of the lightguide 110. For example, a mounting structure of the optical emitter maybe mechanically shifted or moved relative to the input end of the lightguide 110. In another example, the optical emitter may be gimbal-mountedallowing selective tilting of the optical emitter to provide timemultiplexing of the non-zero propagation angle of the guided light beam104.

FIG. 4A illustrates a time-multiplexed light source 120 in an example,according to an embodiment consistent with the principles describedherein. As illustrated in FIG. 4A, the time-multiplexed light source 120comprises a pair of time-multiplexed optical emitters 122′, 122″. Afirst optical emitter 122′ of the pair is configured to provide theguided light beam 104′ at the first non-zero propagation angle and asecond optical emitter 122″ of the pair is configured to provide theguided light beam 104″ at the second non-zero propagation angle. Thedifferent propagation angles of the guided light beam 104′, 104″ mayresult from a difference in a relative location of the first and secondoptical emitters 122′, 122″ relative to a tilted reflector 124, asillustrated for example. The tilted reflector 124 may be a tiltedcollimating reflector, for example. Switching between (i.e., selectiveturning on and off) the first optical emitter 122′ and the secondoptical emitter 122″ as a function of time may be configured to providethe guided light beam 104′, 104″ during respective first and second timeintervals, according to various embodiments. As illustrated in FIG. 4A,a solid line represents the guided light beam 104′ during the first timeinterval from the first optical emitter 122′, while a dashed linerepresents the guided light beam 104″ during the second time intervalfrom the second optical emitter 122″, by way of example.

In some embodiments, the optical emitter 122 of the time-multiplexedlight source 120 may include, but is not limited to, a light emittingdiode (LED) and a laser. For example, the first and second opticalemitters 122′, 122″ may include an LED of a particular color (e.g., red,green, blue) to provide monochromatic light. In some embodiments, anoptical emitter 122 of the pair may comprise a plurality of opticalemitters configured to provide a plurality of different colors of light.For example, the optical emitter 122 may comprise a first LED configuredto provide red light, a second LED configured to provide green light,and a third LED configured to provide blue light. According to someembodiments in which different colors of light are provided by theoptical emitters 122 of the time-multiplexed light source 120, the lightguide 110 may be further configured to guide light beams representingthe different colors of light at different color-specific, non-zeropropagation angles (e.g., in addition to the first and second non-zeropropagation angles associated with the time multiplexing). For example,when the time-multiplexed light source 120 is configured to provide redlight, green light and blue light, each of the red light, the greenlight and the blue light may be provided as a different color,collimated light beam. Further, the light guide 110 may be configured toguide each of the different color collimated light beams at a respectivedifferent color-specific, non-zero propagation angle. In otherembodiments, the time-multiplexed light source 120 may be a broadbandlight source such as, but not limited to, a fluorescent light and awhite LED or more generally a polychromatic LED configured to providebroadband light (e.g., white or polychromatic light).

FIG. 4B illustrates a time-multiplexed light source 120 in an example,according to another embodiment consistent with the principals describedherein. In particular, as illustrated in FIG. 4B, the time-multiplexedlight source 120 comprises the optical emitter 122 configured to emitlight. The time-multiplexed light source 120 of FIG. 4B furthercomprises a time-multiplexed collimator 126. The time-multiplexedcollimator 126 is configured to collimate the emitted light and toprovide the collimated emitted light as the guided light beam 104.According to various embodiments, the time-multiplexed collimator 126has a first collimation state configured to provide the collimatedemitted light at the first non-zero propagation angle during the firsttime interval. Further, the time-multiplexed collimator 126 has a secondcollimation state configured to provide the collimated emitted light atthe second non-zero propagation angle during the second time interval.The first and second collimation states may be provided by mechanicalmotion of the time-multiplexed collimator 126, according to someembodiments. For example, the time-multiplexed collimator 126 maycomprise a tilted collimating reflector (e.g., as illustrated in FIG.4B) having a tilt angle that is variable to provide first and secondcollimation states.

Referring again to FIGS. 3A and 3B, the time-multiplexed backlight 100further comprises a diffraction grating 130. The diffraction grating 130may be a member of a plurality or array of diffraction gratings 130spaced apart from one another in the direction of propagation (boldarrows 103) of the guided light beam 104, e.g., as illustrated in FIG.3A. The diffraction grating 130 is configured to diffractively coupleout a portion of the guided light beam 104 as a coupled-out light beam102. According to various embodiments, the coupled-out light beam 102has a different principal angular direction in each of the first timeinterval and the second time interval. Moreover, the time interval-baseddifferent principal angular directions of the coupled-out light beam 102in the first time interval and the second time interval correspond torespective ones of the first non-zero propagation angle and the secondnon-zero propagation angle of the guided light beam 104, e.g., accordingto equation (1) above.

Further, the diffraction grating 130 (or diffraction gratings 130 of theplurality) is optically coupled to the light guide 110. In particular,by definition, the diffraction grating 130 is located within an opticalfield of the guided light beam 104 within the light guide 110 to enablediffractive coupling out of the guided light beam portion. According tosome embodiments, the diffraction grating 130 may be located at (e.g.,on, in or otherwise adjacent to) a surface of the light guide 110. Atthe surface, the diffraction grating 130 is within an evanescent portionof the optical field of the guided light beam 104 enabling diffractivecoupling out. For example, the diffraction grating 130 may be located onthe first surface 110′ of the light guide 110, as illustrated in FIG.3A. In another example (not illustrated), the diffraction grating 130may be adjacent to the second surface 110″ of the light guide 110. Inother embodiments (also not illustrated), the diffraction grating 130may be located within the light guide 110; that is, the diffractiongrating 130 may be located between the first and second surfaces 110′,110″ of the light guide) to provide diffractive coupling out of theguided time-multiplexed light beam portion.

Referring to FIG. 3B, an extended arrow (solid line) depicts orrepresents the guided light beam 104′ propagating in the light guide 110during the first time interval. Another extended arrow (dashed line) inFIG. 3B depicts the guided light beam 104″ propagating in the lightguide 110 during the second time interval. During the first timeinterval, the guided light beam 104′ is illustrated as having the firstnon-zero propagation angle γ′ and during the second time interval, theguided light beam 104″ is illustrated as having the second non-zeropropagation angle γ″. Further, both of the first and second timeinterval guided light beams 104′, 104″ are illustrated incident on thediffraction grating 130 from their respective different propagationangles γ′, γ″. Also illustrated in FIG. 3B is a first coupled-out lightbeam 102′ (solid line) corresponding to the guided light beam 104′during the first time interval and a second coupled-out light beam 102″(dashed line) corresponding to the guided light beam 104″ in the secondtime interval. The first coupled-out light beam 102′ has a differentprincipal angular direction than a principal angular direction of thesecond coupled-out light beam 102″, as illustrated.

According to some embodiments, the diffraction grating 130 may comprisea multibeam diffraction grating 130. The multibeam diffraction grating130 may be configured to diffractively couple out the portion of theguided light beam 104 as a plurality of coupled-out light beams 102(e.g., as illustrated in FIG. 3A). Further, the coupled-out light beams102 diffractively coupled out by the multibeam diffraction grating 130have different principal angular directions from one another, accordingto various embodiments (e.g., also as illustrated in FIG. 3A). Inparticular, the multibeam diffraction grating 130 may be configured toprovide a first plurality of coupled-out light beams 102 having a firstset of different principal angular directions during the first timeinterval. Further, the multibeam diffraction grating 130 is configuredto provide a second plurality of coupled-out light beams 102 having asecond set of different principal angular directions during the secondtime interval.

FIG. 3A illustrates the first plurality of coupled-out light beams 102comprising first coupled-out light beams 102′ (solid lines) during thefirst time interval and the second plurality of coupled-out light beams102 comprising second coupled-out light beams 102″ (dashed lines) duringthe second time interval provided by the multibeam diffraction grating130. Further, as illustrated in FIG. 3A, the coupled-out light beams102′, 102″ of the first and second pluralities are angularly interleavedwith one another, by way of example and not limitation. The first andsecond sets of different principal angular directions are a function,respectively, of the first and second non-zero propagation angles of thecorresponding guided light beams 104′ and 104″, according to variousembodiments.

FIG. 5A illustrates a cross sectional view of a multibeam diffractiongrating 200 in an example, according to an embodiment consistent withthe principles described herein. FIG. 5B illustrates a perspective viewof a multibeam diffraction grating 200 in an example, according to anembodiment consistent with the principles described herein. Themultibeam diffraction grating 200 illustrated in FIGS. 5A-5B mayrepresent the diffraction grating 130 of FIGS. 3A and 3B, for example.In particular, the illustrated multibeam diffraction grating 200 may beoptically coupled to a light guide 210 with an incident guidedtime-multiplexed light beam 204, as illustrated. The light guide 210 andan incident guided time-multiplexed light beam 204 may be substantiallysimilar to the light guide 110 and the guided light beam 104, forexample.

Further, as illustrated, the multibeam diffraction grating 200 may beconfigured to diffractively couple out a portion of the guidedtime-multiplexed light beam 204 provided by a time-multiplexed lightsource (e.g., the time-multiplexed light source 120) as a plurality ofcoupled-out light beams 202 directed away from the multibeam diffractiongrating 200, as illustrated in FIGS. 5A-5B. The plurality of coupled-outlight beams 202 may be substantially similar to the plurality ofcoupled-out light beams 102, described above for example. In particular,a coupled-out light beam 202 of the plurality may have principal angulardirection that differs from principal angular directions of othercoupled-out light beams 202 of the plurality.

According to various embodiments, the multibeam diffraction grating 200illustrated in FIGS. 5A-5B comprises a plurality of diffractive features220 that may represent one or both of grooves and ridges spaced apartfrom one another, for example. Further, each of the coupled-out lightbeams 202 of the plurality may have a different principal angulardirection determined by characteristics of the diffractive features 220of the multibeam diffraction grating 200, according to variousembodiments. Moreover, according to various embodiments, the differentprincipal angular directions of the coupled-out light beams 202 maycorrespond to different view directions of a multiview display, forexample.

In particular, the diffractive features 220 of the multibeam diffractiongrating 200 are configured to provide diffraction. The provideddiffraction is responsible for the diffractive coupling of the portionof the guided time-multiplexed light beam 204 out of the light guide210. According to some embodiments, the multibeam diffraction grating200 may be or comprise a chirped diffraction grating. By definition, the‘chirped’ diffraction grating is a diffraction grating exhibiting orhaving a diffraction spacing d of or between the diffractive features(i.e., a diffraction pitch) that varies across an extent or length ofthe chirped diffraction grating, e.g., as illustrated in FIGS. 5A-5B(and also in FIG. 3A, for example). Herein, the varying diffractionspacing d is defined and referred to as a ‘chirp’. As a result of thechirp, the portion of the guided time-multiplexed light beam that isdiffractively coupled out propagates away from the chirped diffractiongrating at different diffraction angles corresponding to differentpoints of origin across the chirped diffraction grating of the multibeamdiffraction grating 200. By virtue of a predefined chirp, the chirpeddiffraction grating is responsible for the predetermined and differentprincipal angular directions of the coupled-out light beams 202 of thelight beam plurality.

In some examples, the chirped diffraction grating of the multibeamdiffraction grating 200 may have or exhibit a chirp of the diffractivespacing d that varies linearly with distance. As such, the chirpeddiffraction grating is a ‘linearly chirped’ diffraction grating, bydefinition. FIGS. 5A-5B illustrate the multibeam diffraction grating 200as a linearly chirped diffraction grating, by way of example and notlimitation. In particular, as illustrated therein, the diffractivefeatures 220 are closer together at a first end of the multibeamdiffraction grating 200 than at a second end. Further, the diffractivespacing d of the illustrated diffractive features 220 varies linearlyfrom the first end to the second end, as illustrated therein.

In another example (not illustrated), the chirped diffraction grating ofthe multibeam diffraction grating 200 may exhibit a non-linear chirp ofthe diffractive spacing. Various non-linear chirps that may be used torealize the multibeam diffraction grating 200 include, but are notlimited to, an exponential chirp, a logarithmic chirp or a chirp thatvaries in another, substantially non-uniform or random but stillmonotonic manner. Non-monotonic chirps such as, but not limited to, asinusoidal chirp or a triangle or sawtooth chirp, may also be employed.Combinations of any of these types of chirps may also be employed.

According to some embodiments, the multibeam diffraction grating 200 maycomprise diffractive features 220 that are one or both of curved andchirped. For example, as illustrated in FIG. 5B, the multibeamdiffraction grating 200 comprises diffractive features 220 that are bothcurved and chirped (i.e., the multibeam diffraction grating 200 in FIG.5B is a curved, chirped diffraction grating). Further illustrated inFIG. 5B, the guided time-multiplexed light beam 204 is represented by abold arrow pointing in an incident direction relative to the multibeamdiffraction grating 200 at a first end of the multibeam diffractiongrating 200. Also illustrated is the plurality of coupled-out lightbeams 202 represented by arrows pointing away from the light-incidentside the multibeam diffraction grating 200. The coupled-out light beams202 propagate away from the multibeam diffraction grating 200 in aplurality of different predetermined principal angular directions. Inparticular, the predetermined different principal angular directions ofthe coupled-out light beams 202 are different from one another in bothazimuth and elevation, as illustrated therein. According to variousexamples, both the predefined chirp of the diffractive features 220 andthe curve of the diffractive features 220 may be responsible for thedifferent predetermined principal angular directions of the coupled-outlight beams 202.

According to some embodiments of the principles described herein, adisplay (e.g., an electronic display) is provided. In variousembodiments, the display is configured to emit modulated light beams aspixels of the display. A plurality of pixels, in turn, may represent orprovide a view of the display. Further, in various examples, the emittedmodulated light beams may be preferentially directed toward a viewingdirection of the display. In some embodiments, the display is amultiview electronic display. Different ones of the modulated,differently directed light beams may correspond to different ‘views’associated with the multiview electronic display, according to variousexamples. The different views may provide a ‘glasses free’ (e.g.,autostereoscopic) representation of information being displayed by themultiview electronic display, for example.

FIG. 6 illustrates a block diagram of a multiview display 300 in anexample, according to an embodiment consistent with the principlesdescribed herein. In various embodiments, the multiview display 300 mayalso be referred to as a multiview electronic display. As illustrated,the multiview display 300 is configured to emit light beams 302representing pixels corresponding to different views associated withdifferent view directions of the multiview display 300. Further, aplurality of emitted or ‘coupled-out’ light beams 302 may be emittedduring a corresponding plurality of different time intervals. Inparticular, first emitted or coupled-out light beams 302′ may be emittedduring a first time interval, and second emitted or coupled-out lightbeams 302″ may be emitted during a second time interval, according tovarious embodiments. In some embodiments, the emitted or coupled-outlight beams 302 may be modulated emitted or coupled-out light beams 302,e.g., as described below.

As illustrated in FIG. 6, the multiview display 300 comprises atime-multiplexed light source 310. The time-multiplexed light source 310is configured to provide a light beam having a first non-zeropropagation angle during a first time interval and a second non-zeropropagation angle during a second time interval. The first non-zeropropagation angle is different the second non-zero propagation angle,according to various embodiments. The time-multiplexed light source 310may be substantially similar to the time-multiplexed light source 120described above with respect to the time-multiplexed backlight 100, insome embodiments.

For example, the time-multiplexed light source 310 may comprise a pairof time-multiplexed optical emitters. A first optical emitter of thepair may be configured to provide the light beam 304 at the firstnon-zero propagation angle during the first time interval (depicted as asolid-line arrow) and a second optical emitter of the pair beingconfigured to provide the light beam 304 (depicted as a dashed-linearrow) at the second non-zero propagation angle during the second timeinterval. The time-multiplexed light source 310 may be substantiallysimilar to the time-multiplexed light source 120 illustrated inabove-described FIG. 4A, for example.

In another example, the time-multiplexed light source 310 may comprise atime-multiplexed collimator configured to provide the light beam as acollimated light beam. The time-multiplexed collimator has a firstcollimation state configured to provide the collimated light beam at thefirst non-zero propagation angle and a second collimation stateconfigured to provide the collimator light beam at the second non-zeropropagation angle. For example, the time-multiplexed light source 310may be substantially similar to the time-multiplexed light source 120illustrated in FIG. 4B, described above.

According to various embodiments, the multiview display 300 illustratedin FIG. 6 further comprises a multibeam backlight 320. The multibeambacklight 320 is configured to emit a portion of the light beam 304 fromthe time-multiplexed light source 310 as a first plurality ofcoupled-out light beams 302 (e.g., solid line arrows) during the firsttime interval and as a second plurality of coupled-out light beams 302(e.g., dashed line arrows) during the second time interval,respectively. Further, according to various embodiments, the first andsecond coupled-out light beam pluralities have corresponding first andsecond sets of principal angular directions determined respectively bythe first and second non-zero propagation angles of the light beam fromthe time-multiplexed light source 310. The principal angular directionsare or correspond to view directions of different views of the multiviewdisplay, according to various embodiments. In some embodiments (e.g., asillustrated in FIG. 6), the coupled-out light beams 302 of the first andsecond pluralities of coupled-out light beams are angularly interleavedwith one another. Similarly, the different views of the multiviewdisplay 300 in each of the first and second time intervals may beangularly interleaved, in some embodiments.

In some embodiments, the multibeam backlight 320 may comprise a platelight guide configured to guide the light beam 304 from thetime-multiplexed light source 310. In particular, the light beam 304 maybe guided at the first non-zero propagation angle during the first timeinterval and at the second non-zero propagation angle during a secondtime interval. Further, the time-multiplexed light source 310 may beoptically coupled to an input of the plate light guide, according tovarious embodiments. According to some embodiments, the plate lightguide may be substantially similar to the light guide 110 of thetime-multiplexed backlight 100, described above.

For example, the plate light guide may be a slab optical waveguide thatis a planar sheet of dielectric material configured to guide light bytotal internal reflection. The guided light beam 304 may be guided ateither the first or second non-zero propagation angles as a beam oflight. Thus, the guided light beam 304 guided by the plate light guidemay be substantially similar to the guided light beam 104 of thetime-multiplexed backlight 100. For example, the guided light beam 304may be a collimated light beam, according to some embodiments.

In some embodiments, the multibeam backlight 320 may further comprise anarray of multibeam diffraction gratings optically coupled to the platelight guide. According to various embodiments, a multibeam diffractiongrating of the array may be configured to diffractively couple out aportion of the guided light beam 304 as the first plurality ofcoupled-out light beams 302 during the first time interval (e.g., solidline arrows) and as the second plurality of coupled-out light beams 302during the second time interval (e.g., dashed line arrows). According tosome embodiments, the multibeam diffraction grating of the array may besubstantially similar to the multibeam diffraction grating 130 of thetime-multiplexed backlight 100 as well as the multibeam diffractiongrating 200 (FIGS. 5A-5B), described above. For example, a multibeamdiffraction grating of the array of multibeam diffraction gratings maycomprise a chirped diffraction grating or a chirped diffraction gratinghaving curved diffractive features.

According to some embodiments (e.g., as illustrated in FIG. 6), themultiview display 300 may further comprise a light valve array 330. Thelight valve array 330 is configured to modulate the coupled-out lightbeams 302 of the first and second pluralities to produce respectivemodulated coupled-out light beams 302′, 302″. According to variousembodiments, the modulated coupled-out light beams 302 represent pixelsof the different views of the multiview display 300. In someembodiments, the different views are divided into a first set of viewscorresponding to the first time interval and a second set of viewscorresponding to the second time interval. Further, the view directionsof the first and second sets of views may be angularly interleaved withone another, according to some embodiments. In various examples,different types of light valves in the light valve array 330 may beemployed including, but not limited to, one or more of liquid crystal(LC) light valves, electrowetting light valves, and electrophoreticlight valves. In FIG. 6, the arrows associated with modulatedcoupled-out light beams 302 with dashed lines depict modulatedcoupled-out light beams 302″ of the second plurality and the arrowsassociated with modulated coupled-out light beams 302 with solid linesrepresent the modulated coupled-out light beams 302′ of the firstplurality.

In some embodiments, some coupled-out light beams 302 of the first andsecond pluralities may be configured to pass through the same lightvalves (not illustrated) of the light valve array 330. For example, acoupled-out light beam 302 of the first plurality and anothercoupled-out light beam 302 of the second plurality may be configured topass through or ‘share’ the same light valve, even though thecoupled-out light beams 302 have different principal angular directions.In such embodiments, the light valve may modulate the first pluralitycoupled-out light beam 302 during the first time interval differentlyfrom the second plurality coupled-out light beam 302. Such time-intervaldependent modulation may facilitate time-multiplexed representation ofdifferent views of the multiview display 300, for example. Moreover,light valve sharing between coupled-out light beams 302 of the first andsecond pluralities may increase (e.g., substantially double) aresolution of the multiview display 300 for a given light valveresolution, according to some embodiments.

According to some embodiments of the principles described herein, amethod of time-multiplexed backlight operation is provided. FIG. 7illustrates a flow chart of a method 400 of time-multiplexed backlightoperation in an example, according to an embodiment consistent with theprinciples described herein. As is illustrated in FIG. 7, the method 400of time-multiplexed backlight operation comprises providing 410 atime-multiplexed light beam in a light guide of a backlight where theprovided 410 light beam is guided. Providing 410 a time-multiplexedlight beam comprises introducing a first light beam into the light guideusing a time-multiplexed light source to propagate at a first non-zeropropagation angle during a first time interval; and introducing a secondlight beam into the light guide using the time-multiplexed light sourceto propagate at a second non-zero propagation angle during a second timeinterval. The first and second time intervals are different from oneanother. Moreover, the first and second non-zero propagation angles aredifferent from one another.

In some embodiments, the time-multiplexed light beam may be provided 410using a time-multiplexed light source substantially similar to thetime-multiplexed light source 120 described above with respect to thetime-multiplexed backlight 100, according to some embodiments. Forexample, the time-multiplexed light source may be implemented using atime-multiplexed optical emitters as illustrated in FIG. 4A or with atime-multiplexed collimator as illustrated in FIG. 4B. Further, thelight guide and the guided time-multiplexed light beam may besubstantially similar to the light guide 110 and the guided light beam104, described above with respect to the time-multiplexed backlight 100.In particular, in some embodiments, the light guide may guide the guidedlight according to total internal reflection (e.g., as a collimated beamof light). Further, the provided 410 light beam may be guided at thefirst and second non-zero propagation angles between a first surface anda second surface of the light guide. The light guide may be asubstantially planar dielectric optical waveguide (e.g., a plate lightguide), in some embodiments.

The method 400 of time-multiplexed backlight operation further comprisesdiffractively coupling out 420 a portion of the guided time-multiplexedlight beam as a coupled-out light beam using a diffraction grating. Inparticular, the portion is diffractively coupled out 420 during thefirst time interval and the second time interval using the diffractiongrating. According to various embodiments, the coupled-out light beam isdirected away from a surface of the light guide at time interval-baseddifferent predetermined principal angular directions. Further, thepredetermined principal angular direction in each of the first timeinterval and the second time interval corresponds to a respective one ofthe first non-zero propagation angle and the second non-zero propagationangle of the guided time-multiplexed light beam, according to variousembodiments.

In some embodiments, diffractively coupling out 420 a portion of theguided time-multiplexed light beam comprises using a diffractiongrating, for example, a diffraction grating that is substantiallysimilar to the diffraction grating 130 described above with respect tothe time-multiplexed backlight 100. Further, the coupled-out light beammay be substantially similar to the coupled-out light beam 102 (i.e.,light beams 102′, 102″), also described above. In some embodiments, thediffraction grating may comprise a multibeam diffraction grating. Themultibeam diffraction grating may be substantially similar to themultibeam diffraction grating 200 described above. In particular, themultibeam diffraction grating may be configured to diffractively coupleout 420 the portion of the guided time-multiplexed light beam as aplurality of coupled-out light beams. The coupled-out light beams of thecoupled-out light beam plurality may have different principal angulardirections from one another, according to various embodiments. Also, thecoupled-out light beams in the first time interval generally havedifferent principal angular directions from the coupled-out light beamsduring the second time interval. Further, the different principalangular directions of the coupled-out light beams may correspond torespective view directions of different views of a multiview electronicdisplay, in some embodiments.

In some embodiments (e.g., as illustrated in FIG. 7), the method 400 oftime-multiplexed backlight operation further includes modulating 430 thecoupled-out light beam using a light valve. The modulated 430coupled-out light beam may form a pixel of an electronic display,according to various embodiments. In some embodiments (e.g., where amultibeam diffraction grating is used), modulating 430 the coupled-outlight beam may provide modulation of a plurality of differently directedcoupled-out light beams using a plurality of light valves. Moreover, themodulated 430 differently directed coupled-out light beams may bedirected in different ones of various view directions of the multiviewelectronic display, for example. Further, the different views maycomprise a first set of views during the first time interval and asecond set of views in the second time interval, according to someembodiments. In addition, the first set of views may be angularlyinterleaved with the second set of views, in some embodiments.

The light valve used in modulating 430 the coupled-out light beam may besubstantially similar to a light valve of the light valve array 330,according to some embodiments. For example, the light valve may includea liquid crystal light valve. In another example, the light valve may beanother type of light valve including, but not limited to, one or bothof an electrowetting light valve and an electrophoretic light valve, orcombinations thereof with liquid crystal light valves or other lightvalve types.

Thus, there have been described examples of a time-multiplexed basedbacklight, a multiview display and a method of time-multiplexedbacklight operation that employ time interval-based light at differentnon-zero propagation angles from a time-multiplexed light source. Itshould be understood that the above-described examples are merelyillustrative of some of the many specific examples and embodiments thatrepresent the principles described herein. Clearly, those skilled in theart can readily devise numerous other arrangements without departingfrom the scope as defined by the following claims.

What is claimed is:
 1. A time-multiplexed backlight comprising: a lightguide configured to guide a beam of light as a guided light beam; atime-multiplexed light source configured to provide to the light guidethe light beam at a first non-zero propagation angle during a first timeinterval and at a second non-zero propagation angle during a second timeinterval; and a diffraction grating configured to diffractively coupleout of the light guide a portion of the guided light beam as acoupled-out light beam having a time-interval-based different principalangular direction in each of the first time interval and the second timeinterval, the time interval-based different principal angular directionscorresponding to respective ones of the first non-zero propagation angleand the second non-zero propagation angle of the guided light beam. 2.The time-multiplexed backlight of claim 1, wherein the first and secondtime intervals are non-overlapping intervals of time.
 3. Thetime-multiplexed backlight of claim 1, wherein the time-multiplexedlight source comprises a pair of time-multiplexed optical emitters, afirst optical emitter of the pair being configured to provide the guidedlight beam at the first non-zero propagation angle and a second opticalemitter of the pair being configured to provide the guided light beam atthe second non-zero propagation angle, wherein switching between thefirst optical emitter and the second optical emitter as a function oftime is configured to provide the guided light beam during respectivefirst and second time intervals.
 4. The time-multiplexed backlight ofclaim 1, wherein the time-multiplexed light source comprises an opticalemitter configured to emit light and a time-multiplexed collimatorconfigured to collimate the emitted light and to provide the collimatedemitted light as the guided light beam, the time-multiplexed collimatorhaving a first collimation state configured to provide the collimatedemitted light at the first non-zero propagation angle during the firsttime interval and a second collimation state configured to provide thecollimated emitted light at the second non-zero propagation angle duringthe second time interval.
 5. The time-multiplexed backlight of claim 1,wherein the diffraction grating comprises a multibeam diffractiongrating configured to diffractively couple out the portion of the guidedlight beam as a plurality of coupled-out light beams, coupled-out lightbeams of the coupled-out light beam plurality having different principalangular directions from one another, wherein the multibeam diffractiongrating is configured to diffractively coupled out a first plurality ofcoupled-out light beams having a first set of different principalangular directions in the first time interval and a second plurality ofcoupled-out light beams having a second set of different principalangular directions in the second time interval, the first set and thesecond set being different.
 6. The time-multiplexed backlight of claim5, wherein the first and second non-zero propagation angles of theguided light beam are configured to provide coupled-out light beams ofthe first plurality of coupled-out light beams angularly interleavedwith coupled-out light beams of the second plurality of coupled-outlight beams.
 7. The time-multiplexed backlight of claim 5, wherein themultibeam diffraction grating comprises a chirped diffraction grating.8. The time-multiplexed backlight of claim 5, wherein the multibeamdiffraction grating comprises curved diffractive features adjacent to asurface of the light guide, the curved diffractive features comprisingone of grooves and ridges that are spaced apart from one another at thelight guide surface.
 9. The time-multiplexed backlight of claim 5,wherein the different principal angular directions of coupled-out lightbeams of the respective first and second pluralities of coupled-outlight beams correspond to respective view directions of different viewsof a multiview electronic display.
 10. A multiview electronic displaycomprising the time-multiplexed backlight of claim 5, the multiviewelectronic display further comprising a light valve configured tomodulate a coupled-out light beam of the coupled-out light beamplurality, wherein the principal angular directions of the firstplurality of coupled-out light beams corresponds to a first set of viewdirections of the multiview electronic display, the principal angulardirections of the second plurality of coupled-out light beamscorresponding to a second set of view directions of the multiviewelectronic display, the modulated light beam representing a pixel of themultiview electronic display in the view direction of one of the firstset of view directions and the second set of view directionsrespectively during the first time interval and the second timeinterval.
 11. A multiview display comprising: a time-multiplexed lightsource configured to provide a light beam having a first non-zeropropagation angle during a first time interval and a second non-zeropropagation angle during a second time interval that is different fromthe first non-zero propagation angle; and a multibeam backlightconfigured to emit a portion of the light beam as a first plurality ofcoupled-out light beams during the first time interval and as a secondplurality of coupled-out light beams during the second time interval,the first coupled-out light beam plurality having a first set ofdifferent principal angular directions, the second coupled-out lightbeam plurality having a second set of different principal angulardirections, the first and second sets being different and beingdetermined respectively by the different first and second non-zeropropagation angles of the light beam, wherein the principal angulardirections are view directions of different views of the multiviewdisplay.
 12. The multiview display of claim 11, wherein coupled-outlight beams of the first and second pluralities are angularlyinterleaved with one another.
 13. The multiview display of claim 11,wherein the time-multiplexed light source comprises a pair oftime-multiplexed optical emitters, a first optical emitter of the pairbeing configured to provide the light beam at the first non-zeropropagation angle during the first time interval, a second opticalemitter of the pair being configured to provide the light beam at thesecond non-zero propagation angle during the second time interval. 14.The multiview display of claim 11, wherein the time-multiplexed lightsource comprises a time-multiplexed collimator configured to provide thelight beam as a collimated light beam, the time-multiplexed collimatorhaving a first collimation state configured to provide the collimatedlight beam at the first non-zero propagation angle and having a secondcollimation state configured to provide the collimated light beam at thesecond non-zero propagation angle.
 15. The multiview display of claim11, wherein the multibeam backlight comprises: a plate light guideconfigured to guide the light beam at the first non-zero propagationangle during the first time interval and at the second non-zeropropagation angle during a second time interval; and an array ofmultibeam diffraction gratings optically coupled to the plate lightguide, a multibeam diffraction grating of the array being configured todiffractively couple out the portion of the light beam as the firstplurality of coupled-out light beams during the first time interval andas the second plurality of coupled-out light beams during the secondtime interval, wherein the time-multiplexed light source is opticallycoupled to an input of the plate light guide.
 16. The multiview displayof claim 15, wherein a multibeam diffraction grating of the array ofmultibeam diffraction gratings comprises a chirped diffraction gratinghaving curved diffractive features.
 17. The multiview display of claim11, further comprising a light valve array configured to modulate thecoupled-out light beams of the first and second pluralities ofcoupled-out light beams, the modulated coupled-out light beamsrepresenting pixels of the different views of the multiview display,wherein the different views are divided into a first set of viewscorresponding to the first time interval and a second set of viewscorresponding to the second time interval, view directions of the firstand second sets of views being angularly interleaved with one another.18. A method of time-multiplexed backlight operation, the methodcomprising: providing a time-multiplexed light beam to be guided in alight guide at a first non-zero propagation angle during a first timeinterval and at a second non-zero propagation angle during a second timeinterval using a time-multiplexed light source; and diffractivelycoupling out a portion of the guided time-multiplexed light beam as acoupled-out light beam during the first time interval and the secondtime interval using a diffraction grating, the coupled-out light beambeing directed away from a surface of the light guide at timeinterval-based different predetermined principal angular directions,wherein the predetermined principal angular direction in each of thefirst time interval and the second time interval corresponds to arespective one of the first non-zero propagation angle and the secondnon-zero propagation angle of the guided time-multiplexed light beam.19. The method of time-multiplexed backlight operation of claim 18,wherein the first and second time intervals are separate,non-overlapping intervals of time.
 20. The method of time-multiplexedbacklight operation of claim 19, wherein the diffraction gratingcomprises a multibeam diffraction grating configured to diffractivelycouple out the portion of the guided time-multiplexed light beam as aplurality of coupled-out light beams during each of the first and secondtime intervals, the coupled-out light beams of the coupled-out lightbeam plurality having different principal angular directions from oneanother, the coupled-out light beam plurality in the first time intervalhaving a different set of different principal angular directions fromthe set of different principal angular directions of the coupled-outlight beam plurality in the second time interval.
 21. The method oftime-multiplexed backlight operation of claim 18, wherein the differentprincipal angular directions of the respective coupled-out light beamscorrespond to respective view directions of different views of amultiview electronic display, the different views comprising a first setof views during the first time interval and a second set of views in thesecond time interval.
 22. The method of time-multiplexed backlightoperation of claim 18, further comprising modulating the coupled-outlight beam during the first time interval and the second time intervalusing a light valve, the modulated coupled-out light beam forming apixel an electronic display.